primary parallax
absolute stereoscopic parallax


In the above illustration, the principal points of the photographs can be accepted as the nadir positions. Both the top and base objects are clearly visible. The absolute stereoscopic parallax is 12.36 mm in this case, i.e., the sum of the distances of the corresponding images from their respective nadirs. Differential parallax in this case is the difference in the absolute stereoscopic parallax at the top and base objects being measured, i.e., 12.3−12.32 = 0.04.
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